Two nursing home outbreaks of respiratory infection with Legionella sainthelensi

OBJECTIVE: To describe outbreaks of infection caused by Legionella sainthel ensi occurring in older residents of two nursing homes and to determine ris k factors for the development of infection. DESIGN: Descriptive epidemiology and a case-control study. SETTING: Two nursing homes (140 beds and 254 beds in nursing homes A and B, respectively) located in southern Ontario, Canada, experiencing outbreaks of respiratory tract infection in July and August 1994. SUBJECTS: Case-residents of the two nursing homes who met clinical and labo ratory criteria for Legionella infection. Control-residents were defined as those who were in the homes during the outbreaks and were asymptomatic. MEASUREMENTS: Active surveillance was conducted in both nursing homes to id entify symptomatic residents. Residents with fever or respiratory tract sym ptoms had nasopharyngeal swabs taken for viral antigen detection and cultur e, urine for Legionella antigen detection, and acute and convalescent serol ogy for viruses, Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionell a. Chest X-rays were performed, and an attempt was made to obtain blood and sputum cultures. Water samples from shower heads, faucets, and air conditi oning units were collected for Legionella culture and polymerase chain reac tion (PCR) assay. A case-control study was done to assess possible risk fac tors for legionellosis. RESULTS: Twenty-nine cases - 17 in nursing home A; 12 in nursing home B - w ere identified. Four (14%) case-residents had documented pneumonia and four case-residents died. Univariate analysis revealed that a history of stroke (odds ratio (OR) 2.3 (95% CI, 1.0-5.3)), eating pureed food (OR 4.6 (95% C I, 1.6-12.7)), and having fluids administered with medication (OR 2.5 (95% CI, 1.0-5.9)) were significant risk factors. Cases were less likely to wear dentures (OR .4 (95% CI, .2-.9)) or to eat solid food (OR .3, (95% CI, .1- .6)). Only eating pureed food remained significant in a multivariable analy sis (OR 4.6 (95% CI, 1.6-13.0, P = .01)). CONCLUSION: This report describes outbreaks of legionellosis in two nursing homes, representing the first reported outbreaks of infection caused by Le gionella sainthelensi. The association with illness of dietary characterist ics indicative of swallowing disorders suggests that aspiration was the mos t likely mode of infection. The diagnosis of legionellosis should be consid ered during outbreaks of respiratory infection in nursing homes.